Adding System.Activities Reference In Visual Studio

Hello,

I am trying to create a custom activity using Visual Studio 2019 community edition. The target framework for the class library that I am creating is .Net Core 3.1.

I need to add the System.Activities reference to my class library to create the custom activity. However, when I try to browse and search for System.Activities in NuGet Packages, I do not find System.Activities.

I will appreciate any help in knowing how to add the System.Activities reference.

Regards,
Abhimanyu